Commutator



Patented Apr. 7, 1953 COMMUTA'IOR Charles W. Baechler, Jr., 'Glenolden, and Foster N. Reynolds, Upper Darby, Pa, assignors to Raymond Rosen Engineering Products vInc., Philadelphia, Pa., a corporation of Pennsyl- Vania Application February 18, 1950, Serial No. 146,504

7 Claims.

This invention relates to mechanical switching devices or commutators, and more particularly to adevice for reliably carrying out a large number of continuous switching operations.

Devices capable of performing continuous switching operations are known to the art. The conventional types are not capable of handling a large number of continuous, simultaneous switching operations without occupying a relatively large space and without being relatively complex, thus limiting their use to relatively large apparatus. Commutators known to the present art produce electrical noise in associated circuits when the brushes pass over the contacts or segments; this noise becoming a disturbing factor when carrying out switching operations involving low voltage information-bearing signals.

Another disadvantage of present-day commutators is the presence of varying thermoelectric potentials produced in the brush take-off circuit by the intimate contact of dissimilar metals in the presence of heat. These spurious potentials impair the accuracy of electrical-databearing signals switched by said commutators, especially if said electrical data is transmitted at a low potential level.

Lubrication between contacts and brushes and the selection of materials therefor have also presented much difficulty.

Another problem has been to maintain an accurate control of the phase relations in the signals undergoing switching operations. Vibration of the brushes as they leave one contact and pass over the intervening space, to the next contact (leaving the brush unsupported as it passes from one contact to the next) causes a change in phase relations of said signals undergoing switching operations.

The problem of producing electrical pulses having accurately predetermined duty cycles has been another source of difficulty.

The aforesaid problems in an electrical instrumentation commutator and brush combination (adapted to operate at relatively high speeds for a comparatively long period of time) are inherent in the present art.

Thepresent invention is concerned with overcoming the aforementioned difiiculties and disadvantages encountered with signal-switching devices known to the prior art.

It is the object of this invention to provide a mechanical switching device capable of operating for comparatively long periods of time with,- out maintenance and under adverse conditions.

Another object is to provide a mechanical device for continuous sampling of applied electrical information.

A further object is to provide an arrangement whereby voltages produced by the intimate contact of dissimilar metals in the presence of heat are effectively neutralized.

Another object is to provide a method of producing electrical pulses having an accurately predetermined duty cycle.

Still another object is to provide means for maintaining an accurate control of the phase relations of the signals undergoing switching operations.

Further objects of the invention and novel features of construction and operation will be apparent from the following specification when considered together with the accompanying drawings in which like reference characters indicate like parts.

Figure 1 represents a side-elevational view, partly in cross-section, and slightly less than full-size, of one embodiment of the present in vention; the commutator and brushes and supporting and driving means being shown in crosssection.

Figure 2 represents a vertical cross-sectional view of the commutator plate taken along lines 2-2 of Figure 3 (shown on a substantially enlarged scale).

Figure 3 represents a front elevational view of the commutator plate; viewed along lines 3-4 of Figures 1 and 2 and shown approximately full size.

Figure 4 is a view of the insulated brush-carrying disc and contact wiper arms and brushes; viewed along lines 4-4 of Figure l and shown approximately full size.

Figure 5 represents a fragmentary side view of the brush-carrying disc showing the contact arms damper-springs in relation to the brusharms.

The device illustrated in Figure '1 includes a driving means III, which, in the embodiment shown, is an electrical dynamotor or rotary voltage converter, but can be any suitable electrical motor or other driving means, and a housing II at one or both ends of the motor In, containing a commutator disc or plate 40 and the other parts to be hereinafter described.

The commutator l2, shown in Figures 1, 2 and 3, includes the commutator disc or plate 40, of molded, glass-bonded mica particles having embedded therein a plurality of contacts l3 of predetermined dimensions; said contacts arranged in several circles l1, l8 and I9 and made of coinsilver or other suitable contact materials. One or more rings l4, l and I6, also preferably of coin silver and having corresponding pins 20, 2| and 22 secured thereto for electrical connections, are embedded in the disc 40 and are electrically insulated from each other and from the circles I8 and IQ of contacts l3. A bushing 23 made of steel or other suitable material may be used as a bearing-member or to hold an anti-friction bearing 24 therein; the aforementioned elements being held in their relative po- I may enter to interlock the said rings and the disc 48.

A plurality of contact wiper arms 28, 29, 38, 3|, 32 and 33, made of suitable spring-material having low electrical resistance are supported in juxtaposition to and in contact with said rings and contacts. The wiper arms are formed and disposed in pairs (such as 28 and 29) each pair of arms being fabricated in one piece and being approximately U-shaped. Each pair of contact arms is supported at the base of the U on a circular plate or brush disc 34 by an insulating pad I I 35 and screws 36 and 31.

To raise the natural frequency of the contact arms 28, 3| and 32 which engage the contacts l3, .and to' reduce the vibration thereof, a helper or damper spring 38 engages each of the said arms 28, 3| and 32 which are so located in relation to the disc 40 as to slide over the circles of contacts l9, l8 and Il, respectively.

Each contact wiper arm has soldered or spotwelded to its end a brush 33 made of special brush-material (composed, for instance, of sintered or powdered metals of approximately 70% silver and 30% graphite). The brushes 39 may be silver-plated to facilitate their being soldered or otherwise connected to the arms 28 to 33, inclusive.

The circular plate or brush disc 33, carrying vthe contact wiper arms 28 to 33, is secured to a rotatable shaft 4| by the screws 42, 33 and 34. The shaft 4! may be driven through the gear train 45 by the driving means H) (which is a dynamotor in the embodiment shown but may be any driving means).

The contacts l3, defining the circles I'i, l8 and I9, are electrically insulated from each other by the disc 40, but each contact is closely adjacent the contact on each sideof it. The number of switches (or switching operations) and the character thereof determines the number and size of the individual contacts in each circle l8 and I9, as well as the number of the solid rings 20, 2| and 22 required. The length of duty cycle (that period when any one commutator is connected by a pair of brushes to one of the contacts to produce electrical pulses or to sample electrical intelligence) is determined by the size of the-brushes 39 in relation to the size of the contacts I3. The spacing of the contacts l3 and the size of the brushes 39 are such that the unsupported portion of the brush (as it passes over the contacts) is, at no time, greater than 25% of its arcuate length. This relationship prevents the brush from vibrating by insuring a smooth flowing motion over the contacts.

While in Figure 3 the clearances between the contacts in the circle l9 are shown as being slightly greater than the clearances between the contacts in the circle l8, and the latter slightly greater than the clearances between the contacts in the circle ll, yet in the preferred embodiment of the present invention the clearances between contacts in each of the three circles in substantially the same.

As is shown in Figure l, the commutator I2 is supported in the housing I near the outer end thereof, and restrained against rotation with respect to said housing by the engagement of the pin it in the slot 25. A retaining ring ill may be screw-threadedly secured to the housing H with the flange-portion thereof bearing against the commutator |2 to hold it axially in place. If desired, a gasket may be interposed between the commutator l2 and the flange on the retaining ring 41. When the disc 4!) is in position, as shown in Figure 1, the pins 23, 2| and 22 on the rings l4, l5 and I6, respectively, are disposed outwardly or away from the body-portion l Thus, the head-portion of the contacts l3 and the brush-engaging surface of the rings l4, l5 and I6 are disposed within the housing A gear-train 45, through which the dynamotor rotatably drives the shaft 4|, is also supported within the housing II, with theshaft 3| extending into and rotatably supported in the antifriction bearing 24 in the commutator l2, whereby the shaft 4| may rotate with respect to the commutator. The circular plate or brush-disc 34 is supported on and rotated by the shaft 4| with the brushes 39 resiliently urged against the contacts l3 and the rings 16, I5 and It by the contact-arms 28 to 33, inclusive. Thus, when the dynamotor is actuated to set the gear-train 45 in operation, the brushes 39 are rotated across the contacts l3 and along the rings M, i5 and I6 at an accurately predetermined rate-of-speed.

In actual operation of this embodiment of the present invention, a direct-current of suitable voltage is applied through the terminal 26 (or 2| or 22) to the ring It (or l5 or it). This current is transmitted through the brush 39 and the contact wiper-arms to the head-portion of the contacts |3 in the circle Because the rotating brushes 39 are but momentarily in contact with any one of the contacts l3 (the duration of such period of contact being determined by the lineal speed of the brushes 39, the size of the brush, and-the diameter of the head of the contact adjacent thereto), the electrical pulse will be transmitted intermittently and in sequence to the pro truding extension of the contacts I3. The diameter of each contact i3 is dependent upon the number of contacts in a circle and the diameter of the circle. This electrical pulse may then be conducted, through appropriate wires (not shown), to a measuring, indicating, controlling or recording device. Likewise, an electrical signal may be returned through appropriate wires (not shown) to another one of the contacts l3 (preferably a contact I3 in a different circular row (E8 or IQ) of contacts), said returning electrical pulse then being conducted through another pair of contact arms to another one of the commutator rings (I5 or L6) and the terminal comiected thereto.

- In the present invention, it is not necessary that every one of the contacts 13 which make up one of the rings of contacts l1, H or 13 be a part of an electrical circuit. Thus, that portion of some of the contacts which protrudes beyond or outwardly from the disc 40 may be clipped oil or left electrically unconnected. In such cases, the head-portion 'of said contacts will act only as a spanning-member-or guide-way to carry the brushes 39 between alternate electrically-connected contact-heads.

A specific example is as follows. Twenty-eight pulses having a duty-cycle of 50% and one pulse having a duty-cycle equal to three of the 50% pulses combined are desired for each revolution of the plate 34. A ring of contacts made up of sixty individual contacts I3, as shown by the circle 11, is req'uired, in combination with one solid ring 14. Connection from a D. C. voltage source is made to the pin "20 of the solid ring M. For the wide pulse, three of the contacts l3 in the circle I! are electrically connected through the extensions of the contacts I3 on the outer side of the commutator plate 40. Of the remaining contacts I3 in the circle ll, every alternate protruding portion or pin is removed. The unclippe'd pins are then electrically connected (through wires not shown) whereby an electrical impulse of predetermined duty-cycle may be transmitted.

To produce synchronization pulses of a predetermined duty-cycle, the proper brush length is selected and attached to the wiper arms. If pulse widths are desired which are multiples of others to be produced, several of the individual "contacts (the number depending on the desired pulse width) may be tied together electrically to produce the desired effect, as described above.

The phase relation between any of the previously described operations can be controlled by loosening the screws 36 and 3'1, and slightly shifting the contact-arms and brushes 39.

With the switching device of the present invention, the interference or static commonly known as brush noise is reduced to a very low magnitude.

By utilizing the wiper arm arrangement shown, stray voltages due to thermocouple effect; are canceled out. This is more clearly shown by considering the brush units comprising wiper-arms 32 and 33 and its associated brushes '39 in more detail. The brush 39, composed of silver-graphite, forms, with wiper-arm 32 made of 'Phospor bronze, a thermocouple joint. Similarly, a brush 39 and the wiper arm 33 form another thermocouple joint. When the Phosphor bronze elements are electrically positive with respect 'to the silver-graphite brushes, the brush arrangement is analogous to two batteries, equal in capacity and size, connected electrically opposite to each other. The net result is that the thermocouple voltages due to the intimate contact of the dissimilar metals are effectively neutralized.

Because the switching device of the present invention reduces brush noise and effectively neutralizes the thermocouple voltages, signals of very low potentials may be transmitted or switches without introducing any appreciable error.

The present invention is particularly adapted for rapid and continuous switching or transmitting of electrical impulses. Many types of electrical switching operations are made possible by the present invention. By appropriate selection of contact arms, other arrangements or connections than illustrated and described herein may be made to interconnect rings I4, l5 and i6 and the contacts i 3 in the circles l1, l8 and [9. Thus, the contact arm which engages the ring [4 may transmit an electrical current through a contact arm (like the arm 32) to the circle of contacts 18 or H! rather than the circle of contact H by varying the radial dimension between the ends of the arms 32 and 33.

The contacts I3 and the rings l4, l5 and I6, as well as the bushing 23 are secured in place or molded in situ during the formation of the commutator disc 40. Thus, the rings l4, l5 and I6 and the contacts [3 may be supported in appropriate molds and the commutator disc 40 may be injection-molded around said contacts and said rings.

By using a commutator disc 46 which is molded of glass-bonded mica-particles, a commutator [-2 having highly stable physical characteristics may be produced. Thus, the commutator rings and the contacts may be accurately spaced with relation to one another so that the electrical impulse conducted between the brushes 39 and the contacts 13 or the rings l4, l5 and i6 may have a duty-cycle or span which is accurately predetermined. Because of aforesaid highly stable physical characteristics of the glass-bonded mica commutator disc, accurate spacing of the commutator rings and contacts is maintained despite continuous commutation of signals at high speed for prolonged periods of time. There is neither loosening of the rings or contacts nor any warping of the disc, both of which are responsible for spurious noise signals in rapid commutation of low level informationbearing signals.

Moreover, extraneous, interferring static or stray voltage pulses are effectively eliminated in the device of the present invention whereby accurately controlled signals may be switched or transmitted.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Having described our invention, what we claim as new and desire to protect by Letters Patent is the following:

1. In a mechanical device suited for long-continued and high-speed commutation of electrical pulses or signals, a molded inorganic dielectric commutator disc of glass-bonded mica particles having a plurality of concentric continuous contact rings securely fastened on one side of said disc during the molding operation, each ring having at least one terminal projection connected thereto and passing through said disc and protruding beyond the other side thereof, a plurality of segmented concentric rings formed of spaced contact-members secured in situ during the molding of said disc, some of said contact-members having a terminal portion passing through said disc and projecting beyond the other side thereof, said disc of glass-bonded mica particles permanently tightly holding said continuous contact rings and the contact members of said segmented contact rings with accurate spacing and with the brush-engaging faces of said con- 7 tact rings and contact members permanently in an undistorted plane.

2. In a mechanical device suited for longcontinued and high-speed commutation of electrical pulses or signals, a molded commutator disc of glass-bonded mica particles having a plurality of concentric continuous silver contact rings securely fastened on one side of said disc during the molding operation, each ring having at least one terminal projection connected thereto and passing through said disc and protruding beyond the other side thereof, a plurality of concentric segmented rings formed of spaced silver contact-members secured in situ during the molding of said disc, some of said contact-members having a terminal portion passing through said disc and projecting beyond the other side thereof, said disc of lass-bonded mica particles being effective permanently tightly to hold said continuous contact rings and the contact members of said segmented contact rings with precise spacing and with their brush-engaging surfaces in an undistorted plane.

3. In a mechanical device suited for longcontinued and high-speed commutation of electrical pulses or signals, a molded commutator disc of glass-bonded mica particles having a plurality of concentric continuous contact rings securely fastened on one side of said disc during the molding operation, each rin having lockin means interlockingly to engage said disc and having at least one terminal projection connected thereto and passing through said disc and protruding beyond the other side thereof, a plurality of concentric rings formed of spaced contactmembers secured in situ during the molding of said disc, locking means on said contact-members for interlockingly engagin said disc, some of said contact-members having a terminal portion passing through said disc and projecting beyond the other side thereof, the high stability of the physical characteristics of the glass-bonded mica discs and said locking members insuring permanent precisely fixed spacing in an undistorted plane of the brush-engaging faces of said contact rings and members.

4. A commutator suited for rapid, continuous switching of low voltage signals and characterized by negligible error due to noise and phase-shift com rising a commutator plate of molded glassresilient U-shaped wiper contact mounted at the base of the U upon said support and having resilient arms whose spacing corresponds with the radial spacing of said pair of rings and whose free ends respectively engage said rings. the close spacing of said contact members insuring smooth, vibrationless movement of the corresponding wiper contact arm in avoidance of noise and phase-shift, the high stability of the physical characteristics of said glass-bonded mica plate insuring that the ring surfaces engaged by said contact members are permanently held in an undistorted plane and with invariable spacing.

5. A commutator as in claim 4 in which it is provided that the vibration frequency of the wiper arm engaging said ring of spaced contact members shall be substantially different from the frequency of vibration imparted thereto by its movement over said contact members.

6. A commutator suited for rapid and longcontinued low voltage signals comprising a molded plate of glass-bonded mica particles having securely fastened therein during molding at least one pair of concentric contact rings extending from one face of the plate, one ring of each pair being circumferentially continuous and the other ring of the pair comprising closely angularly spaced contact members, said rings having brush-engaging surfaces continuously maintained in an undistorted plane and with invariable spacing by said plate of glass-bonded mica particles.

7. A commutator suited for long-continued and high-speed commutation of electrical pulses or signals comprising a molded plate of glassbonded mica particles having at least one pair of concentric contact rings securely fastened on one side of said plate during the molding operation, at least one ring of the pair comprising closely angularly spaced contact members, said rings having brush-engaging surfaces continuously maintained in an undistorted plane and with invariable spacing by said plate of glassbonded mica particles.

CHARLES W. BAECHLER, JR. FOSTER N. REYNOLDS.

REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number 

